1. Field of the Invention
This invention relates to a new and improved cooling system using liquid coolant for an internal combustion powered vehicle, and more particularly, to an improved cooling system having an engine warm-up mode with a flow circuit extending: from a coolant pump, then through coolant passages in the cylinder head, through a passenger compartment heat exchanger, and back to the pump whereby flow through coolant passages in the engine block are prevented which isolates these passages to reduce the period of time for warming-up the engine while heat is quickly available for heating the vehicle passenger compartment. After the engine is warmed-up, a single thermostatic control valve located across a down-flow passage between the cylinder head and engine block passages opens in response to increased temperature of coolant in the cylinder head to direct the flow of coolant from the cooling passages of the cylinder head passages to the engine block passages and then through a radiator.
2. Description of Related Art
Prior to the present invention, engine cooling systems have been devised with various cooling circuit arrangements to improve operation of the engine as well as operation of associated units, such as the passenger compartment heater and an associated windowshield defroster.
In application 52-85309 published in Japan as document No. 54-20248 on Feb. 2, 1979, an engine cooling circulation system is disclosed in which a pair of thermostats are employed to isolate the cylinder block and radiator from coolant flow during initial engine operation so that heated coolant flows through the cylinder head and heater for quick warm-up of the passenger compartment.
In S.A.E publications C427/84 and C443/84, both copyrighted in 1984, dual and separate coolant circuits for the cylinder head and engine block are disclosed with the head and block cooled at different coolant temperatures and with reported improved engine performance. The coolant in the cylinder head circuit is maintained at a lower temperature than the engine block coolant to reduce surface temperatures of the combustion chamber so that the fuel mixture burns smoothly and knock is reduced. Lower octane fuel is also tolerated. The higher coolant temperatures in the engine block are effective to keep friction losses low so that operating efficiency is enhanced.
In U.S. Pat. Nos. 4,212,270 and 4,423,705, dual coolant pumps and dual cooling system are disclosed to separately cool the block and the cylinder head.
U.S. Pat. No. 3,981,279 discloses an engine cooling system with a single thermostat with coolant flow from a pump into passages in the engine block, through passages in the cylinder head, through a radiator, and then back to the pump. In this sequential flow system, the advantages of a down-flow system, such as in the present invention, are not obtained. The thermostat controller opens at an elevated temperature to allow coolant to flow from the cylinder head back to the radiator to control the temperature level of the coolant in the block and the head at the same temperature.